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37.5-acre lake near Belvidere. The lake tops out around 44 ft. The depth chart is built from real state fisheries GPS surveys, so the humps, channels and drop-offs you see are measured, not guessed. Species by species, here's what the data says the year looks like.
Drawn out, this is 36 acres of water rimmed by 1.6 miles of bank. The shoreline is moderately structured (index 1.9) — enough points and pockets to pattern. About 41% of the surface sits shallower than 15 ft — that's the weed-and-bait zone. Tip to tip the water measures near 0.6 mi with a 0.3-mi widest point. You'll find it in McHenry County. Closest neighbour on DepthScout: McCullom Lake, 6 mi northwest of here.
Start shallow in spring: largemouth bass sit in 2 to 10 ft that time of year. Warm water sends them out to 8 to 20 ft; cold water stacks them in 15 to 35 ft. Top water on the chart: Shallow bay flat, a weed flat in the 2 ft range, prime in spring. Fish it in early morning and the evening and you'll meet the bite. Throw a texas-rigged 10" worm or a deep-diving crankbait until the fish tell you otherwise.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 10 ft | dawn & dusk | Shallow bay flat (2 ft) | Spinnerbait, Chatterbait |
| Summer | 8 to 20 ft | dawn & dusk | Main-lake point (9 ft) | Texas-rigged 10" worm, Deep-diving crankbait |
| Fall | 4 to 15 ft | midday & dawn | Main-lake point (9 ft) | Squarebill crankbait (shad), Spinnerbait |
| Winter | 15 to 35 ft | midday | Break off the point (23 ft) | Blade bait, Jigging spoon |
Spring puts bluegill in skinny water — 1 to 6 ft is the zone. Warm water sends them out to 4 to 15 ft; cold water stacks them in 10 to 25 ft. Shallow bay flat is the standout, a weed flat at roughly 2 ft, rated prime for spring bluegill. Plan around early morning and the evening in the warm months. A small sponge spider (fly) or a micro tube jig covers the summer program.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 1 to 6 ft | midday & dusk | Shallow bay flat (2 ft) | 1/32 oz jig + micro plastic, Tiny popper (evenings) |
| Summer | 4 to 15 ft | dawn & dusk | Back-bay flat (4 ft) | Small sponge spider (fly), Micro tube jig |
| Fall | 6 to 18 ft | midday | Back-bay flat (4 ft) | Micro jig + waxworm, Small spoon tipped |
| Winter | 10 to 25 ft | midday | Break off the point (23 ft) | Tungsten ice jig + plastic, Tiny spoon |
The spring pattern is a shallow one: crappie in 2 to 8 ft. Midsummer fish sit out in 10 to 25 ft before dropping to 15 to 35 ft for winter. The spot to know is Shallow bay flat, a weed flat in about 2 ft of water that rates prime for crappie in spring. Plan around early morning and the evening in the warm months. Summer baits: a jig trolled/spider-rigged or a small crankbait (trolled) gets it done.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 8 ft | midday & dawn | Shallow bay flat (2 ft) | 1/16 oz jig + tube, Curly-tail grub |
| Summer | 10 to 25 ft | dawn & dusk | Break off the point (23 ft) | Jig trolled/spider-rigged, Small crankbait (trolled) |
| Fall | 8 to 20 ft | dawn | Break off the point (23 ft) | Jig + minnow combo, Small swimbait (1.5-2") |
| Winter | 15 to 35 ft | midday | Deep basin (42 ft) | Tungsten jig + soft plastic, Tiny jigging spoon |
Start shallow in spring: channel catfish sit in 3 to 12 ft that time of year. Warm water sends them out to 8 to 25 ft; cold water stacks them in 20 to 40 ft. Top water on the chart: Deep basin, a deep basin in the 42 ft range, prime in winter. Fish it in after dark and the evening and you'll meet the bite.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 12 ft | dusk | Back-bay flat (4 ft) | |
| Summer | 8 to 25 ft | night & dusk | Break off the point (23 ft) | |
| Fall | 10 to 30 ft | dusk | Break off the point (23 ft) | |
| Winter | 20 to 40 ft | midday | Deep basin (42 ft) |
5 pieces of structure are mapped here — Deep basin, around 42 ft, is the deepest of them.
Season dates, license requirements, and size and bag limits for Illinois waters are set by the Illinois DNR — and special regulations can apply to Boulder Lake specifically, so confirm the current rules before you fish.
Check the official Illinois fishing regulations →
Boulder Lake is about 44 ft (13 m) deep at its deepest point. The depth chart here comes from real state fisheries GPS surveys, so the contours reflect measured depths.
Anglers target largemouth bass, bluegill, crappie, channel catfish on Boulder Lake.
Shallow bay flat is the top-rated area: a weed flat in about 2 ft of water that rates prime for largemouth bass in spring. Scroll up to the map for the complete spot list by species and season.
For largemouth bass, the summer bite is best in early morning and the evening. Each species page section below lists the seasonal windows, and the map shows a live NOW badge when you're inside one.
Fishing on Boulder Lake is regulated by the Illinois DNR. Check the official Illinois regulations for current license requirements, season dates, and size and bag limits — special regulations can apply to this specific water.
McCullom Lake 6 mi · Long Lake 7 mi · Cedar Lake 11 mi · Diamond Lake 11 mi · Sand Lake 12 mi · Peat Lake 14 mi, WI · Elizabeth Lake 15 mi, WI/IL · Rock Lake 15 mi, WI · Cross Lake 15 mi, WI/IL · Lake Mary 16 mi, WI · Camp Lake 16 mi, WI · Voltz Lake 16 mi, WI
See how Boulder Lake stacks up: best largemouth bass lakes in Illinois · best crappie lakes in Illinois · best bluegill lakes in Illinois · best channel catfish lakes in Illinois
Browse all Illinois fishing maps or see every water on DepthScout. Bathymetry credit: state fisheries survey programs. How we build these maps. Fish here with a sonar unit that logs? Send us your depth data and we'll improve this chart, credited to you. For fishing guidance only, never navigation.